RF Microelectromechanical Systems Switches Research Articles

Integration of Niobium Low-Temperature-Superconducting RF Circuits With Gold-Based RF MEMS Switches

A novel eight-mask fabrication process for the integration of low-temperature-superconducting niobium (Nb) RF circuits with gold-based RF microelectromechanical system (MEMS) switches is proposed. DC-contact and capacitive-contact RF MEMS switches integrated with Nb-based transmission lines are presented for the first time. A comparison of the RF performance of the switches at room and cryogenic temperatures indicate that the proposed gold-based MEMS fabrication process did have a major impact on the superconducting characteristics of Nb. A switched capacitor bank is also designed, implementing a dc-contact RF MEMS switch. The measured results of the capacitor bank show the variation of the capacitance value from 0.22 to 5.25 pF at 4 K. A thermal analysis of the devices under test (DUTs) is also performed, and an investigation is carried out to minimize the thermal loss between the chuck and the DUT.

Novel DC-40 GHz MEMS series-shunt switch for high isolation and high power applications

This paper presents the design, fabrication, and characterization of a lateral contact series-shunt ohmic RF microelectromechanical systems (MEMS) switch actuated by an electrothermal actuator. Since the proposed RF MEMS switch is actuated electrothermally, it can be operated at an extremely low operation voltage of 0.16V. In this switch, two series switches are cascaded by a quarter wavelength section of transmission line suspended over the trench of the substrate to form a series-shunt configuration according to the principle of impedance transforming. By using a single bidirectional thermal MEMS actuator to control the signal, the switch provides higher reliability when through high power microwave signal. The measured results show that an insertion loss of 1.2dB or better is achieved from DC-40GHz. The isolation is −50dB at 5GHz, −45dB at 20GHz and −60dB at 35GHz. What is more, this switch also exhibits high linearity, and high power handing for DC-40-GHz applications. In the switch OFF state, self-actuation does not happen up to the input power of 40dBm at 1GHz. In the switch ON state, no significant insertion loss variations or problems in the contacts, due to the RF power, can be observed below 31dBm input power.

Effect of Environmental Humidity on Dielectric Charging Effect in RF MEMS Capacitive Switches Based on $C$– $V$ Properties

A capacitance-voltage (C- V) model is developed for RF microelectromechanical systems (MEMS) switches at upstate and downstate. The transient capacitance response of the RF MEMS switches at different switch states was measured for different humidity levels. By using the C -V model as well as the voltage shift dependent of trapped charges, the transient trapped charges at different switch states and humidity levels are obtained. Charging models at different switch states are explored in detail. It is shown that the injected charges increase linearly with humidity levels and the internal polarization increases with increasing humidity at downstate. The speed of charge injection at 80% relative humidity (RH) is about ten times faster than that at 20% RH. A measurement of pull-in voltage shifts by C- V sweep cycles at 20% and 80 % RH gives a reasonable evidence. The present model is useful to understand the pull-in voltage shift of the RF MEMS switch.

Cantilever Beam Metal-Contact MEMS Switch

We present a new design of a miniature RF microelectromechanical system (MEMS) metal-contact switch and investigate various aspects associated with lowering the pull-down voltage and overcoming the stiction problem. Lowering the pull-down voltage in this design is based on reducing the spring constant by changing the cantilever beam geometry of the RF MEMS switch, and the stiction problem is overcome by a simple integrated method using two tiny posts located on the substrate at the free end of the cantilever beam.

RF MEMS DPDT Switch Using Novel Simulated Seesaw Design

This paper investigates an RF MEMS (Radio Frequency Micro Electro-Mechanical System) switch from DC to 5.8 GHz switching, for use in mobile communications systems and devices. The RF MEMS switch uses a novel seesaw design to create a Double-Pole Double-Throw (DPDT) Switch which increases the capabilities of the seesaw design structure. A low Switching supply voltage with high RF isolation was achieved during its development. After looking at other available seesaw designs, it was discovered that an improvement could be attained by adding additional contacts. An improved concept over existing Single-Pole Single-Throw (SPST) seesaw switches was achieved by using a DPDT switch with a set of upper and lower contacts at each side of the seesaw. To conform to the Microscale, from 1 μm – 100 μm, a length of 41μm was chosen to provide an adequate size for fabrication. Copper Bulk General (Cu) was chosen for the pivot material due to its good electrical conductivity and sufficient flexibility for elastic recovery. A working simulation was achieved without compromising the ‘Air-Gap’ between the contacts, which retains high isolation when the switch is open-circuited. The electrostatic supply voltage has been significantly reduced to a value which is closer to that used in mobile devices.

RF MEMS Switch and Its Applications

RF MEMS (Radio Frequency Microelectromechanical System) has seen an amazing growth in the past 20 years. It has immense commercial and defense potential due to its low loss, low power consumption and superior RF performances. In this article, RF MEMS and its applications are reviewed. Special emphasis is on the RF MEMS switches and MEMS phase shifters investigated in IMETU (Institute of Microelectronics of Tsinghua University). A variety of RF MEMS switches with different configurations are introduced. The MEMS switch present unique properties for the application in future miniaturized antenna and radar system. The prototype illustrates the RF MEMS switch as a fundamental structure in signal path control, structural optimization, and match circuits is very promising to be used in future reconfigurable radar and antenna system, which will address to the application not only in the mobile terminal but also the high end wireless sensor network.

RF MEMS Switchable Slot Patch Antenna Integrated With Bias Network

The functionality of the patch antenna with switchable slot (PASS) is realized by integrating a commercially packaged MEMS (microelectromechanical system) switch and a novel bias network. The proposed antenna includes the fully integrated dc bias network capable of actuating the MEMS switch on the slot. The bias network can minimize the interference between dc bias and RF radiation mechanism with a negligible loss. By using a MEMS switch and the bias network, the patch antenna operates at 4.57 GHz and 4.88 GHz. The fabricated design shows acceptable return losses and directivities at the broadside direction when the switch is on and off. The influence of RF MEMS switch on the antenna impedance and radiation pattern is addressed.

Miniature MEMS Switches for RF Applications

This paper presents a new way to design MEMS (microelectromechanical system) metal contact switches for RF applications using miniature MEMS cantilevers. A single 25 × 25 μm switch is first demonstrated with a Au-to-Ru contact, Cu = 5 fF and Ron = 7 Ω at an actuation voltage of 55 V. The measured switching time is 2.2 μs and the release time is <;1 μs. The switch is robust to stress effects (residual and stress gradients) which increases its yield on large wafers. To reduce the effective switch resistance, 10-20 miniature RF MEMS switches have been placed in parallel and result in equal current division between the switches, an up-state capacitance of 30-65 fF and a down-state resistance of 1.4-1.5 Ω. Furthermore, 10-20 element back-to-back switch arrays are developed and result in a marked improvement in the reliability of the overall switching device. A series-shunt design is also demonstrated with greatly improved isolation. The device has a figure-of-merit of fc = 1/(2πRonCu) = 3.8 THz (RonCu = 42 fs).

Microstructure evolution of gold thin films under spherical indentation for micro switch contact applications

RF MEMS (Radio Frequency Micro Electro Mechanical System) switches are promising devices but their gold-on-gold contacts, assimilated for this study to a sphere/plane contact, represent a major reliability issue. A first step toward understanding failure mechanisms is to investigate the contact metal microstructure evolution under static and cyclic loading. After static and cyclic loading of sputtered gold thin films under spherical indentation, high-resolution Electron Back Scatter Diffraction (EBSD) is used to investigate the contact area. Grain rotation against {111} fiber texture of 1-μm-thick sputtered gold thin film is a signature of plastic deformation. Grain rotation is observed above 1.6 mN under static loading using a spherical diamond indenter with 50-μm tip radius. The heterogeneity in grain rotation observed corresponds to a greater plastic deformation in the middle of the indent than at the edge. A 30° grain rotation due to cyclic work hardening is observed for a half-million mechanical cycles under 300 μN load using a spherical gold tip (20 μm radius). The same test in hot switching mode induces a grain growth in the contact area. Therefore, thermal effects occurring during hot switching are underlined.

An RF MEMS switch with a differential gap between electrodes for high isolation and low voltage operation

A double-actuation RF microelectromechanical system (MEMS) switch with high isolation and low voltage operation for RF and microwave applications is presented. The operation voltage of the suggested double-actuation vertical RF MEMS switch structure was reduced without decreasing the actuation gap. Theoretically, the operation voltage of the suggested structure is about 29% lower than that of a single-actuation vertical RF MEMS switch with the same fabrication method, electrode area and equal contact gap. The proposed RF MEMS switch was fabricated by surface micromachining with seven photo-masks on a quartz wafer. To achieve planarization and the stair-like structure, a polyimide sacrificial layer was spin-coated, cured and etched in two steps and patterned by a dry etching step which defines the double-actuation mechanism. The measured results of the fabricated RF MEMS switch demonstrate that the insertion loss was lower than 0.11 dB for the 20 V ON state, the isolation was higher than 39.1 dB for the OFF state and the return loss was better than 32.1 dB for the 20 V ON state from dc to 6 GHz. The minimum pull-in voltage of the fabricated RF MEMS switch was 10 V.

Capacitive RF MEMS Switches With Tantalum-Based Materials

In this paper, shunt capacitive RF microelectromechanical systems (MEMS) switches are developed in III-V technology using tantalum nitride (TaN) and tantalum pentoxide (Ta <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</sub> ) for the actuation lines and the dielectric layers, respectively. A compositional, structural, and electrical characterization of the TaN and Ta <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</sub> films is preliminarily performed, demonstrating that they are valid alternatives to the conventional materials used in III-V technology for RF MEMS switches. Specifically, it is found that the TaN film resistivity can be tuned from 0.01 to 30 Ω · cm by changing the deposition parameters. On the other hand, dielectric Ta <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</sub> films show a low leakage current density of few nanoamperes per square centimeter for E ~ 1 MV/cm, a high breakdown field of 4 MV/cm, and a high dielectric constant of 32. The realized switches show good actuation voltages, in the range of 15-20 V, an insertion loss better than -0.8 dB up to 30 GHz, and an isolation of ~-40 dB at the resonant frequency, which is, according to bridge length, between 15 and 30 GHz. A comparison between the measured S-parameter values and the results of a circuit simulation is also presented and discussed, providing useful information on the operation of the fabricated switches.

A 1.2–1.6-GHz Substrate-Integrated-Waveguide RF MEMS Tunable Filter

This paper presents a high-performance substrate-integrated-waveguide RF microelectromechanical systems (MEMS) tunable filter for 1.2-1.6-GHz frequency range. The proposed filter is developed using packaged RF MEMS switches and utilizes a two-layer structure that effectively isolates the cavity filter from the RF MEMS switch circuitry. The two-pole filter implemented on RT/Duroid 6010LM exhibits an insertion loss of 2.2-4.1 dB and a return loss better than 15 dB for all tuning states. The relative bandwidth of the filter is 3.7 &amp;#x00B1; 0.5% over the tuning range. The measuredQuof the filter is 93-132 over the tuning range, which is the best reportedQin filters using off-the-shelf RF MEMS switches on conventional printed circuit board substrates. In addition, an upper stopband rejection better than 28 dB is obtained up to 4.0 GHz by employing low-pass filters at the bandpass filter terminals at the cost of 0.7-1.0-dB increase in the insertion loss.

A systematic reliability investigation of the dielectric charging process in electrostatically actuated MEMS based on Kelvin probe force microscopy

This paper presents a comprehensive investigation for the dielectric charging problem in electrostatically actuated microelectromechanical system (MEMS) devices. The approach is based on Kelvin probe force microscopy (KPFM) and targets, in this specific paper, thin PECVD silicon nitride films for electrostatic capacitive RF MEMS switches. KPFM has been employed in order to mimic the potential induced at the dielectric surface due to charge injection through asperities. The effect of dielectric thickness has been investigated through depositing SiNx films with different thicknesses. Then, in order to simulate the different scenarios of dielectric charging in real MEMS switches, SiNx films have been deposited over thermally grown oxide, evaporated gold and electroplated gold layers. Also, the effect of the deposition conditions has been investigated through depositing dielectric films using low and high frequency PECVD methods. The investigation reveals that thin dielectric films have larger relaxation times compared to thick ones when the same injection bias is applied, independently of the substrate nature. For the same SiNx film thickness, the decay time constant is found to be smaller in dielectric films deposited over metallic layers compared to the ones deposited over silicon substrates. Finally, the material stoichiometry is found to affect the surface potential distribution as well as the relaxation time constant.

Charge Carriers Injection/Extraction at the Metal-Polymer Interface and Its Influence in the Capacitive Microelectromechanical Systems-Switches Actuation Voltage

Opposite results concerning the sign of the parasitic charge accumulated at the metal dielectric contact in RF microelectromechanical systems (MEMS) capacitive switches are found in the literature. The mechanism concerning charge injection/extraction at the metal-dielectric contact and its influence on the pull-in voltage needs to be further clarified. A model-switch, for which only one dimension is in the microns range, is used to study the behaviour of a capacitive RF MEMS switch. The aim is to analyze how the electric charge is injected/extracted into or from the dielectric material under the applied field and to obtain realistic data to understand how this parasitic charge influences the pull-in voltage Vpi and the pull-off voltage Vpo. A triangle voltage is employed to measure Vpi and Vpo, by measuring the isothermal charging/discharging currents. Our results demonstrate that Vpi is strongly dependent on the injected/extracted charge on the free surface of the dielectric. The charge injected/extracted at the bottom side of the dielectric has no influence on the actuation voltage. The charge injected/extracted on the free surface of the dielectric determines an increase of the modulus of Vpi and, eventually, the switch can fail to actuate. An estimation of the charge stored into the material was obtained (i) by measuring the charging current and the discharging current and (ii) from the value of the Vpi. The parasitic charge necessary to keep the bridge stick to the insulator is 5.3 x 10(-4) C m(-2) for our experimental conditions. The modification of the Vpi determined by the stored charge in the dielectric is analyzed. An increase of the relative dielectric permittivity by a factor of 2 produces a decrease of the actuation voltage of 10%. A variation of 30% in the elastic constant determines a variation of about 20% in the Vpi. A voltage threshold for charge injection/extraction was not observed.

Capacitive RF MEMS Switches Fabricated in Standard 0.35-$\mu{\hbox{m}}$ CMOS Technology

The objective of this paper is to investigate the integration of capacitive type RF microelectromechanical systems (MEMS) switches in a standard CMOS technology. A maskless monolithic integration process dedicated to electrostatically actuated capacitive type RF MEMS switches is developed and optimized. The fabricated switches consist of composite metal-dielectric warped membranes. The warped-plate structure is used to increase the capacitance ratio of the switch. The switches are fabricated using the interconnect metal and dielectric layers available in a standard 0.35-μm CMOS process. Measurement results for the first switch show an insertion loss less than 0.98 dB, a return loss below 13 dB up to 20 GHz in the up-state, and a down-state isolation of 12.4-17.9 dB from 10 to 20 GHz. The capacitance ratio is enhanced up to 91:1 using the warped-plate structure. A second cascaded switch consisting of two shunt capacitive switches and a slow-wave high-impedance transmission line section is designed and fabricated for high-isolation applications. The measured insertion loss for this switch is less than 1.41 dB up to 20 GHz, the return loss is below 19 dB, and the isolation is 19-40 dB across the frequency band from 10 to 20 GHz. The proposed RF MEMS switches can be used in millimeter-wave CMOS RF front-ends where multiband functionality and reconfigurability is required.

Thermally Actuated Latching RF MEMS Switch and Its Characteristics

Here, a new thermally actuated latching wideband RF microelectromechanical systems (MEMS) switch is presented. The switch employs two thermal actuators connected to two thin metal arms which serve as signal lines of coplanar waveguide switch. The actuators pull the thin arms sequentially, and latch the switch. The switch can be actuated on and off by using either short voltage or current pulses. Using a dielectric bridge (nitride) as an interface between the actuators and the thin arms, the RF circuitry is separated from DC actuators, allowing wide-band operation. The switch demonstrates an excellent wideband RF performance with an insertion loss of better than 0.3 dB up to 20 GHz and better than 0.8 dB up to 40 GHz. The return loss and isolation of the switch is better than 20 dB for the entire frequency band. The switch also has a very satisfactory repeatability with better than 0.1-dB variation in insertion loss and less than 1-dB variation in return loss and isolation at 30-dB level up to 6000 times switching cycles. The switch has been also successfully tested for RF power handling capability up to 40 dBm. The proposed switch has very simple RF structure which makes it an ideal candidate to be integrated in the form of more complex circuitry. An application of the proposed switch for a band selection network which is used in multiband transceivers has been presented here.

Frequency Scalable Model for MEMS Capacitive Shunt Switches at Millimeter-Wave Frequencies

This paper presents an approach to RF microelectromechanical systems (MEMS) capacitive shunt switch design from <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">K</i> -band up to <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">W</i> -band based on the scalability of the RF MEMS switch with frequency. The parameters of the switch's equivalent-circuit model also follow scaling rules. The measurement results of the fabricated switches show an excellent agreement with simulations that allow to validate the MEMS model in the entire band from 20 up to 94 GHz. This model is going to be used in the phase shifter circuit design for antenna array applications. The first 60-GHz phase shifter results are also reported here.

Thick membrane operated rf microelectromechanical system switch with low actuation voltage

Most researcher who have studied the radio frequency (rf) microelectromechanical system (MEMS) switch has focused on the electrostatic actuation types switch because of this type’s low power consumption, simple fabrication method, and good rf characteristics compared to magnetic, thermal, and piezoelectric driving method. However, most of electrostatic actuation type switch needs high operation voltage compared to other types. One of the reasons that affect the high operation voltage is the bending of the membrane because of an internal stress gradient. This bending increases the gap between electrode and membrane. To solve this problem, the authors developed the thick membrane operated seesaw type rf MEMS switch. This membrane consisted of a pivot under single crystal thick silicon membrane for a seesaw mode operation and a flexible spring for an up-down actuation mode. After the fabrication of this switch, the authors measured its rf characteristics. The minimum actuation voltage was about 12V, the isol...

A configurable L/S‐band integrated elliptical lowpass filter utilizing MEMS technology

AbstractIn this article, the design, analysis, and implementation of a dual band 1 GHz/3 GHz elliptical filter utilizing a micro‐electro‐mechanical systems (MEMS) switch is introduced. The band selection is achieved via MEMS‐switch configurable capacitor structures. The RF MEMS switch uses thermal actuation and is separately fabricated and characterized; the switch achieves an insertion loss of 0.7 dB and an isolation of 45 dB. The elliptical filter is implemented using active frequency‐dependent negative resistor (FDNR) structures. The filter achieves 29 dB of rejection at a 500 MHz offset from the 944 MHz corner, and 26.2 dB of rejection at a 1 GHz offset from the 3.06 GHz corner. © 2008 Wiley Periodicals, Inc. Microwave Opt Technol Lett 50: 2791–2794, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.23828

A 25–75-MHz RF MEMS Tunable Filter

This paper presents a state-of-the-art discrete RF microelectromechanical systems (MEMS) tunable filter designed for 25-75-MHz operation. This paper also presents an enhanced model of the RF MEMS switch, which is used for accurate prediction of the tunable filter response. The two-pole lumped-element filter is based on digital capacitor banks with on-chip metal-contact RF MEMS switches and lumped inductors, and results in a tuning range of 3:1 with fine frequency resolution, and a return loss better than 13 dB for the entire tuning range. The relative bandwidth of the filter is 4 plusmn 1% over the tuning range and the insertion loss is 3-5 dB, limited mostly by the inductor Q and the switch loss. The IIP <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> measurements prove that tunable filters with metal-contact series RF MEMS switches show extremely linear behavior (IIP <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> > 68 dBm).